stripes
This approximately circular complex just over 1 km in diameter intrudes faulted and folded Palaeozoic shales, sandstones and cherts. The complex appears to have a poorly defined ring structure with an outer ring of syenite and fenite and a central area chiefly of nepheline syenite with smaller bodies of ijolite, melteigite, pyroxenite and jacupirangite. Near the centre a breccia with a calcite cement outcrops and carbonatite has been encountered in a number of boreholes. Carbonatite is also present as dykes and irregular masses near the margins of the intrusion. Highly weathered rocks averaging 13 m in thickness cover much of the complex but the outer parts of the nepheline syenite form a low ridge. The fenites are dominated by aegirine which may comprise 80-90% of the rock and these pass into syenites which are probably also fenites, and essentially orthoclase (80-98%) rocks. The nepheline syenites contain alkali feldspar, about 32% nepheline and 7% garnet. The ijolite series varies from rocks with 60% nepheline to jacupirangite with only traces, one variety of which consists principally of biotite with a little magnetite and sphene. Pyroxenite consists of ferro-augite/aegirine-augite with some biotite but the pyroxene in the melteigites is aegirine-augite. One melteigite type contains 30-60% Ti-garnet, which is present throughout the ijolite series. The carbonatites are calcite rocks with accessory biotite, aegirine, magnetite, pyrite and pyrrhotine. Although dykes are common within the complex they are even more abundant within the surrounding sediments and include phonolites, trachytes, ouachitites, monchiquites and fourchites. Apart from the fenites shown on Fig. 170, a thermal aureole extends for a further 300 m or more and involves hornfelsing of shales, while nearer the complex more siliceous rocks contain cristobalite, wollastonite, tremolite, aegirine, miserite and calcite. Palaeomagnetic data will be found in Scharon and Hsu (1969).
FRYKLUND, V.C., HARNER, R.S. and KAISER, E.P. 1954. Niobium (columbium) and titanium at Magnet Cove and Potash Sulphur Springs, Arkansas. Bulletin, United States Geological Survey, 1015-B: 23-57.
HOLLINGSWORTH, J.S. 1967. Geology of the Wilson Springs vanadium deposits Garland County, Arkansas. Guidebook, Geological Society of America Field Conference, Central Arkansas Economic Geology and Petrology. Arkansas Geological Commission, Little Rock: 22-8.
SCHARON, L. and HSU, I-C. 1969. Paleomagnetic investigation of some Arkansas alkalic igneous rocks. Journal of Geophysical Research, 74: 2774-9